There are many reasons why it is beneficial to ascertain the roughness of a print media surface such as a paper surface. For example, in manufacturing processes, it is desirable for paper to be of a generally uniform roughness. By ascertaining the roughness of a paper surface, one can ascertain whether paper that is mass produced has a uniform degree of roughness. In printing processes, roughness determinations can assist in setting certain printing parameters, such as the amount of toner that is used and the toner parameters that govern the toner's use.
In manufacturing scenarios, there have been methods and systems evolve for ascertaining the roughness of a paper surface. One typical method is the so-called Parker Surface Roughness Test (Print Surf) method. This method measures the air which passes between the surface of a coated paper and a flat surface of either steel or rubber. The apparatus that is used to carry out such a test is very expensive, is not portable, and requires a laboratory staff and space. More importantly the test lacks a high resolution for the smoothest surfaces.
In printing scenarios (such as electrostatographic reproduction of images, e.g. electrophotography, and laser printing, as well as thermal ink jet, and thermal transfer reproduction of images), copy quality is sensitive to and can be affected by the level of roughness of the paper. Distinct variations can exist as to the level of paper roughness found in individual copy sheets, such as paper, that are used in printing devices. Additionally, individuals using such printing devices are typically free to switch the print media or paper upon which printing takes place. For example, in an office environment, less expensive draft paper might be used for preparing draft versions of different documents, while more expensive paper might be used for final versions of the documents. The characteristics of these different types of paper, including roughness, can vary widely.
Various machine parameters can be affected by the roughness of the paper to be processed through the machine. Based on the paper's roughness level, these parameters can be adjusted for their optimum functionality within the machine as well as for achieving optimum copy quality. For example, an ideal goal in electrophotography is to have the correct amount of toner deposited onto a copy sheet on a continuous basis. With poor development control two situations occur. First, concerning a variability of toner quantity applied, too little toner creates lighter images, where too much toner creates darker images and may cause toner to appear in non-image areas. Second, concerning the machine, too much toner development causes excess toner waste which increases the expense of running the machine. Replacement of these components is thereby required on a more frequent basis. The need for precise toner control is intensified in color development systems where individual color images are superimposed on each other to create the full color image.
A rougher paper surface contains a greater surface area than a smoother paper surface, and may therefore require application of a higher developed toner mass per unit area to get the same dark, uniform, sharp copy quality. Additionally, if a greater amount of toner is required on a rougher paper surface, the development voltage, and/or the toner concentration, and/or the fuser set temperature must be raised to assure that the toner is completely fused to the paper. Under-fused toner on a substrate creates toner adhesion and durability issues which can include smears, flaking toner at paper folds, and integrity during handling. An increased voltage may also be required for the corona generating devices associated with both the charging element, as well as the transfer element, for a rougher surface paper requiring a greater amount of toner deposited thereon. Uniformly increasing machine parameters such as the fuser set temperature, fuser dwell time, or voltage level to the charging device, transfer device or developer may eliminate certain copy quality problems on rougher surface papers, however, other negative factors can be created. For example, increased stress on these affected components causes the need for more frequent component repair or replacement. Furthermore, the increased power required to run the component at the higher settings can result in increased energy consumption and cost. Machines that can optimize copy quality as well as internal processing operations will have a greater latitude of operation and a competitive edge.
Several widely used, indirect, methods of paper surface roughness measurement, characterized as Sheffield smoothness, Bekk smoothness and Parker Print Surf (described above), include air leak techniques which measure the volume of air that leaks, over a fixed time interval, between the paper surface and a test equipment seal, or, conversely, the time required for the leakage of a fixed air volume. Although these indirect surface roughness measurement methods offer a numerically quantified, relative value of surface roughness, they have not proven to be consistent, reliable indicators of print quality.
Accordingly, this invention arose out of concerns associated with providing improved methods and systems for ascertain the roughness of a print media surface.